Airworthiness Directive · Amendment 39-16764 · Equipment/furnishings
The Boeing Company Model 747-400 and -400F Series Airplanes
This AD applies to The Boeing Company Model 747-400 and -400F series airplanes, certificated in any category, as identified in Boeing Alert Service Bulletin 747-25A3588, Revision 1, dated April 7, 2011.
We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires a general visual inspection for cracks and holes of the main equipment center (MEC) drip shields, and repairs if necessary; installation of a fiberglass reinforcing overcoat; and, for certain airplanes, installation of stiffening panels to the MEC drip shields. This AD was prompted by a report of a loss of bus control unit number 1 and generator control units numbers 1 and 2 while the airplane was on the ground, and multiple operator reports of cracked MEC drip shields. We are issuing this AD to prevent water penetration into the MEC, which could result in the loss of flight critical systems.
Comply with this AD within the compliance times specified, unless already done.
Within 24 months after the effective date of this AD, do the actions specified in paragraph (g)(1) or (g)(2) of this AD, as applicable, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 747-25A3588, Revision 1, dated April 7, 2011.
(1) For Group 1 and Group 3 airplanes, as identified in Boeing Alert Service Bulletin 747-25A3588, Revision 1, dated April 7, 2011: Do a general visual inspection of the MEC drip shield to detect cracking and holes, do all applicable repairs, and install the MEC drip shield panel stiffeners and the fiberglass reinforcing overcoat to the MEC drip shield, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 747-25A3588, Revision 1, dated April 7, 2011. Do all applicable repairs before further flight.
(2) For Group 2 airplanes, as identified in Boeing Alert Service Bulletin 747-25A3588, Revision 1, dated April 7, 2011: Do a general visual inspection of the MEC drip shield to detect cracking and holes, do all applicable repairs, and install the fiberglass reinforcing overcoat to the MEC drip shield, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 747-25A3588, Revision 1, dated April 7, 2011. Do all applicable repairs before further flight.
Accomplishing the actions required in paragraph (g) of this AD before the effective date of this AD in accordance with Boeing Alert Service Bulletin 747-25A3588, dated July 19, 2010, is considered acceptable for compliance with the corresponding actions specified in this AD.
